The present invention relates to curable silicone coatings containing silicone resins. More particularly the present invention relates to curable silicone coatings containing silicone resins in which the resins are prepared by a continuous method whereby the ratio of reactants is kept constant thus producing less variation in the final silicone resin that is produced. The silicone resins produced by the unique methods disclosed herein provide beneficial properties when added to curable silicone coatings.
The use of silicone resins in silicone release coatings has been described in the art. For example, Keil, in U.S. Pat. No. 3,527,659 teaches the use, in a silicone release composition of a copolymer of R.sub.3 SiO.sub.1/2 units and SiO.sub.2 units having no more than 0.6 weight percent of silicon-bonded hydroxy groups, where R denotes a monovalent hydrocarbon radical having no more than 2 carbon atoms. Sandford, in U.S. Pat. No. 4,123,604 teaches the use of a similar copolymer of R.sub.3 SiO.sub.1/2 units, SiO.sub.2 units, and (CH.sub.2 .dbd.CH)R.sub.2 SiO.sub.1/2 units wherein R denotes a monovalent hydrocarbon radical having no more than 2 carbon atoms in silicone release compositions curable by the addition of methylhydrogenpolysiloxanes to silicon-bonded vinyl groups which provide intermediate range release characteristics.
European Patent Application No. 0108208 teaches that unsaturated organic monomers such as alpha-olefins are employed as carrier diluents to assist in introducing high levels of vinyl resins having R.sub.3 SiO.sub.1/2 units and SiO.sub.2 units into solventless silicone release compositions. It is further taught that the silicone resin acts as a controlled release additive allowing adjustment of the release (i.e. the force in grams required to separate an adhesive from a substrate coated with a cured release coating) of the silicone release compositions.
Blizzard in U.S. Pat. No. 4,322,518 teaches a composition comprising a liquid copolymeric organopolysiloxane and a vinyl or hydroxyl containing polydiorganosiloxane where the liquid copolymeric organosiloxane is prepared by forming a homogenous mixture of an organic solvent solution of a resinous copolymeric siloxane containing silicon-bonded hydroxy radicals and consists of R.sub.3 SiO.sub.1/2 units and SiO.sub.2 units where R is a hydrocarbyl radical and the ratio of R.sub.3 SiO.sub.1/2 units to SiO.sub.2 units is 0.6-0.9/1 and a liquid organohydrogenpolysiloxane, and then heating the homogenous mixture. Blizzard further discloses that the composition is used for coating paper to give controllable release of adhesives thereto.
Melancon in U.S. Pat. No. 4,533,575 discloses a process comprising the steps of forming a curable organosilicon composition by mixing an ethylenically unsaturated polysiloxane, a polysiloxane, a metal containing hydrosilylation catalyst, a 1,4 dicarboxylic acid compound as an inhibitor, and optionally an MQ resin release modifier.
Rivers-Farrell et al. in U.S. Pat. No. 4,611,042 disclose a xylene-soluble, resinous copolymer containing SiO.sub.2 units, trimethylsiloxane units, and alkenyldimethylsiloxane units such as 5-hexenyldimethylsiloxane units. The resinous copolymer is disclosed as being useful as a component in silicone coatings, especially silicone release coatings, to provide intermediate range release forces against adhesives.
In contrast, the present invention is directed to a curable silicone coating composition containing uniquely prepared silicone resins. None of the references described hereinabove describe a curable silicone coating containing a silicone resin prepared according to the methods disclosed herein.